There are a number of situations in which a reliable waterproof pocket would be desirable. One example is the swimmer visiting the beach. He or she will not wish to leave valuable items such as credit cards and money unattended on the beach while swimming. However, unless there is someone to look after such items this may be unavoidable.
Another example is a diver, either a professional diver or a "social" diver. In addition to valuables, a diver may wish to carry with him or her other items such as papers and maps that should be kept dry.
A waterproof pocket would also be useful in situations where a proposed user does not intend to become completely immersed in water but is likely in any event to become very wet. Persons going salmon fishing, canoeing, sailing or white-water rafting come into this category. Even hikers may appreciate a waterproof pocket in extreme weather conditions.
To date a simple but effective waterproof pocket has yet to appear. Existing pockets are either unreliable or over-complicated in construction.